1. Field of the Invention
The invention concerns a management process and a control arrangement for application of this process to a system made up of cells electrically connected in series which each include one or more electrical energy storage units, as is usual in the art, and more particularly to a control arrangement for a high capacity system likely to be subjected to alternating deep discharge and fast charge phases, for example by virtue of being used as a power source for an electric vehicle.
2. Description of the Prior Art
Storage battery systems of the above kind include a relatively large number of cells because of the quantities of energy that need to be stored. The cells of the same storage battery system, which are usually identical, can have slightly different characteristics and consequently vary slightly in performance. Performance differences between series-connected cells of the same storage battery system can increase significantly with time and in the process of successive charging and discharging. This can seriously degrade the operation of the storage battery system and of the application using it.
One solution to limiting any increase in the differences between cells of a storage battery system is to account for the individual evolution of the cells that constitute the system during charging phases in order to avoid unnecessarily overcharging the units of these cells that reach a full charge first.
A solution of this kind is described in document WO-A-9515023, for example, which provides for individual monitoring and balancing devices in combination with each cell of a system. The monitoring and balancing device are provided in a pack, in which the cells are connected in series. This arrangement enables at least a part of the charging current transmitted to a cell to be bypassed when a measured value, and in particular a measured value of the voltage at the terminals of that cell, reaches a maximal set point value. A controller connected to the devices by a common digital line provides a record of the differences between cells and triggers an alarm.
However, the above described solution kind is not entirely satisfactory. In particular this solution can entail high energy dissipation for balancing during charging, especially fast charging with relatively short balancing times, and where these operations are carried out in a systematically time-invariant manner.